The present invention relates to a magnetic tunnel device incorporating a pair of magnetic layers laminated through a tunnel barrier layer to pass a tunnel current from either of the magnetic layers to another magnetic layer and structured such that the conductance of the tunnel current varies depending on a polarizability of magnetization of the pair of the magnetic layers, a manufacturing method therefor and a magnetic head.
Hitherto, a magnetic tunneling effect has been reported which can be obtained from a layer structure in which a thin insulating layer is held between a pair of magnetic metal layers. In this case, the conductance of a tunnel current which flows in the insulating layer varies depending on the relative angle of the pair of the magnetic metal layers. That is, the layer structure in which the thin insulating layer is held between the pair of the magnetic metal layers has a magnetic resistance effect with respect to the tunnel current which flows in the insulating layer.
The magnetic tunneling effect enables a magnetic resistance ratio to theoretically be calculated from the polarizability of magnetization of the pair of the magnetic metal layers. When Fe is employed as the material of the pair of the magnetic metal layers, a magnetic resistance ratio of about 40% can be expected.
Therefore, the magnetic tunnel device having at least the layer structure in which the thin insulating layer is held by the pair of the magnetic metal layers has attracted attention as a device for detecting an external magnetic field.
A magnetic tunnel device of the foregoing type usually has a structure that metal oxide is employed to constitute the thin insulating layer. If the metal oxide is employed to constitute the insulating layer, a pinhole or the like is, however, formed. In this case, short circuit undesirably occurs between the magnetic metal layers forming the pair. When the metal oxide is employed to constitute the insulating layer, a satisfactory degree of oxidation cannot sometimes be obtained. The tunnel barrier becomes too incomplete to always realize the magnetic tunneling effect.
In view of the foregoing, an object of the present invention is to provide a magnetic tunnel device with which a tunnel current can reliably be introduced into a tunnel barrier layer to exhibit a stable magnetic tunnel effect, a manufacturing method therefor and a magnetic head.
A magnetic tunnel device according to the present invention comprises: first and second magnetic layers laminated though a tunnel barrier layer, wherein the magnetic tunnel device has a region in which change in a magnetic resistance ratio with respect to change in a voltage applied in such a manner that the second magnetic layer has a lower potential as compared with the potential of the first magnetic layer is smaller than change in a magnetic resistance ratio with respect to change in a voltage applied in such a manner that the second magnetic layer has a higher potential as compared with the potential of the first magnetic layer.
The magnetic tunnel device having the above-mentioned structure and according to the present invention is structured such that the voltage is applied in such a manner that the potential of the second magnetic layer is lower than that of the first magnetic layer. Therefore, electrons flow from the second magnetic layer to the first magnetic layer through the tunnel barrier layer. At this time, the quantity of change in the magnetic resistance ratio in the magnetic tunnel device is reduced as compared with a case in which electrons are allowed to flow in an inverse direction. That is, the voltage is applied in such a manner that the potential of the second magnetic layer is lower than that of the first magnetic layer. Thus, the dependency of the magnetic resistance ratio of the magnetic tunnel device on the voltage is inhibited. Therefore, in the magnetic tunnel device, stable tunnel currents flow to the tunnel barrier layer without any dependency on the level of the voltage.
A magnetic tunnel device according to the present invention comprises: a first magnetic layer; a tunnel barrier layer formed on the first magnetic layer and structured such that the degree of oxidation is raised from the first magnetic layer; and a second magnetic layer formed on the tunnel barrier layer, wherein electrons are supplied from the second magnetic layer to the first magnetic layer so that tunnel currents are supplied to the tunnel barrier layer.
The magnetic tunnel device structured as described above and according to the present invention is arranged such that metal is oxidized in stages on the first magnetic layer so that the tunnel barrier layer is formed. That is, the tunnel barrier layer having a lowest degree of oxidation is formed on the first magnetic layer. Therefore, the tunnel barrier layer has a satisfactory adhesiveness with respect to the first magnetic layer. Moreover, the magnetic tunnel device is structured such that a direction in which electrons are supplied to the tunnel barrier layer is determined. Therefore, in the magnetic tunnel device, stable tunnel currents are supplied to the tunnel barrier layer without any dependency on the voltage.
A method of manufacturing a magnetic tunnel device according to the present invention comprises the steps of: forming a first magnetic layer; forming a tunnel barrier layer on the first magnetic layer by oxidizing metal in stages; and forming a second magnetic layer on the first magnetic layer through the tunnel barrier layer.
The method of manufacturing a magnetic tunnel device structured as described above and according to the present invention is arranged such that the tunnel barrier layer is formed by oxidizing metal in stages. Therefore, the adhesiveness of the tunnel barrier layer with respect to the first magnetic layer can be improved. Since the foregoing method is structured such that metal is oxidized in stages to form the tunnel barrier layer, a magnetic tunnel device can be manufactured in which tunnel currents are stably flow without any dependency on the voltage.
A magnetic head according to the present invention comprises: a magnetic tunnel device incorporating first and second magnetic layers laminated though a tunnel barrier layer, wherein the magnetic tunnel device has a region in which change in a magnetic resistance ratio with respect to change in a voltage applied in such a manner that the second magnetic layer has a lower potential as compared with the potential of the first magnetic layer is smaller than change in a magnetic resistance ratio with respect to change in a voltage applied in such a manner that the second magnetic layer has a higher potential as compared with the potential of the first magnetic layer, and the magnetic tunnel device serves as a sensitive portion.
The magnetic bead having the above-mentioned structure and according to the present invention is structured such that the voltage is applied to the magnetic tunnel device in such a manner that the potential of the second magnetic layer is lower than that of the first magnetic layer. Therefore, electrons flow from the second magnetic layer to the first magnetic layer through the tunnel barrier layer. At this time, the quantity of change in the magnetic resistance ratio in the magnetic tunnel device is reduced as compared with a case in which electrons are allowed to flow in an inverse direction. That is, the voltage is applied in such a manner that the potential of the second magnetic layer is lower than that of the first magnetic layer. Thus, the dependency of the magnetic resistance ratio of the magnetic tunnel device on the voltage is inhibited. Therefore, in the magnetic head, the magnetic tunnel device serving as the sensitive portion can stably be operated.
A magnetic head according to the present invention comprises: a magnetic tunnel device incorporating a first magnetic layer; a tunnel barrier layer which is formed on the first magnetic layer and in which the degree of oxidation is raised from the first magnetic layer; and a second magnetic layer formed on the tunnel barrier layer, wherein electrons are supplied from the second magnetic layer to the first magnetic layer to cause tunnel currents to flow to the tunnel barrier layer, and the magnetic tunnel device serves as a sensitive portion.
The magnetic head structured as described above and according to the present invention is arranged such that the magnetic tunnel device having the tunnel barrier layer formed on the first magnetic layer by oxidizing metal in stages serves as the sensitive portion. That is, the tunnel barrier layer having a lowest degree of oxidation is formed on the first magnetic layer. Therefore, the tunnel barrier layer has a satisfactory adhesiveness with respect to the first magnetic layer. Moreover, the magnetic head is structured such that a direction in which electrons are supplied to the tunnel barrier layer is determined. Therefore, in the magnetic heads, stable tunnel currents are supplied to the tunnel barrier layer without any dependency on the voltage. As a result, the magnetic tunnel device serving as the sensitive portion can stably be operated.